The present invention is directed to a novel methodology for an in situ preparation of metal-molybdate catalysts that are useful for methanol oxidation to formaldehyde.
Iron-molybdate catalysts have been manufactured from the coprecipitation of aqueous solutions of FeCl3 and ammonium heptamolybdate. Both of these reagents are expensive and significant amounts of water are required in the commercial manufacture of the iron-molybdate catalysts in accordance with prior manufacturing methods. In addition, during the calcination step required to form the active Fe2(MoO4)3 and MoO3 components, significant amounts of pollutants, such as nitrous oxides (NOx), ammonia (NH3) and hydrochloric acid (HCl) are formed.
Thus, the synthesis of iron-molybdate catalysts prior to the present invention has a number of significant problems. In view of these significant problems, there is a need for new methods of formation for these catalysts. More specifically, there is a need for methods of manufacture of iron-molybdate catalysts that involve more common and less expensive reagents, do not require water, and reduce the formation of pollutants. The present invention fulfills all of these needs. These and other benefits of the present invention are described below.
It has now been discovered that in situ formation of metal-molybdate catalysts can be achieved by beginning the methanol conversion process over a physical mixture comprising: (a) a particulate source of catalytically active metal oxide and (b) a source of molybdenum oxide such as molybdenum trioxide (MoO3). During the course of the methanol conversion reaction, catalytically active metal-molybdate/(MoO3) forms in situ and without the use of water.
For the formation of the preferred iron-molybdate catalysts, a combination of (a) a particulate source of iron oxide such as powdered forms of ferric oxide (Fe2O3), coprecipitated iron molybdate (Fe2(MoO4)3), or other metal oxide such as NiO; and (b) a source of molybdenum oxide such as molybdenum trioxide (MoO3) are loaded into a methanol conversion zone. During the course of the methanol conversion reaction at typical conversion conditions, catalytically active metal molybdate (e.g. (Fe2(MoO4)3)/(MoO3)) forms in situ and without the use of water.
Metal-molybdate catalysts formed by the present invention and the resulting methanol conversion process are comparable to metal-molybdate catalysts formed via the more expensive and polluting manufacturing methods of the prior art. These and other advantages will be readily recognized by those skilled in the art.